A virtual reality system generally consists of a head mounted graphic display connected to a computer, along with a method for communicating to the computer, the exact direction in which the person wearing the head mounted display is facing. The purpose of a virtual reality system is to create for the person wearing the display, the illusion of being in a different location. In order to achieve this, the computer displays the virtual environment as if it were being viewed from both the position and the direction that the person is looking. As the person moves its head and the head mounted display, the computer continuously changes the image being viewed to show the virtual environment from the current perspective. Thus, it appears to the person wearing the display that they are actually in the virtual environment and are looking around.
A variation of this approach can be called telepresence. In this system, instead of a computer generating the image, the image is generated by a controlled, movable video camera. As the person wearing the display moves its head, the camera, in a remote location, moves correspondingly, showing the location from the orientation of the remote viewer. This system thus makes it appear to the viewer that it is actually in the remote location and looking around.
Both of these systems have a serious drawback that reduces the effectiveness of the illusion that the person wearing the display is actually in a different location. The problem is latency. Latency, in this context, is defined as the time required to calculate the perspective and position from which the viewer is facing, transmit this information to the computer or the remote camera, generate the view from the new orientation, and transmit that view back to the display. Should the latency be long enough, the viewer may be facing a slightly different direction when the image from the earlier sampling is finally displayed. The effect is to make the environment, which should be positionally stable, seem to move. This effect can be troubling and may cause disorientation in some users.
In an effort to overcome this problem, faster sensors, computers and transmission methods have been employed. However, even a small amount of latency reduces the effectiveness of the system. As long as any amount of latency exists, the illusion will not be complete.